Polyhedral boranes, especially decahydrodecaborate [B10H10]2− and dodecahydrododecaborate [B12H12]2− salts are useful compounds for a variety of purposes including for propellant fuels, battery electrolytes, and as precursors to carborane compounds, which have a variety of applications in various fields including the biomedical field. Decahydrodecaborate, dodecahydrododecaborate, and carboranes are stable in air, water, and high temperatures.
Despite the utility and commercial value of polyhedral boranes, potential applications for polyhedral boranes are impeded by the difficulty of manufacturing polyhedral boranes. Existing methods of producing polyhedral boranes present a number of safety concerns. First, some methods rely on the use of toxic and difficult to handle reagents such as diborane, which can explode on contact with air. Second, the pathway to polyhedral boranes proceeds through a large number of intermediates, some of which are highly unstable and can be explosive. Further complicating the reaction, a large amount of flammable gasses, including H2 gas, are produced during the reaction, so the reactions must be conducted to avoid the build up of pressure, and also to dilute the flammable gas to safe levels.
Methods have been developed to avoid the use of diborane, but these methods are low yielding. Most synthetic routes that avoid diborane require an additional isolation step for isolating a boron intermediate prior to reaction of the polyhedral borane. Additional steps are undesirable as they reduce the efficiency of the reaction. Reactions where the complex is not isolated have not proved durable and they often require expensive solvents or catalysts. Moreover, these reactions typically produce unwanted byproducts that are difficult to separate from the polyhedral boranes.
Control of the polyhedral boranes produced has been difficult in prior processes. Control to produce a high yield of a single polyhedral borane has also been difficult. Dodecahydrododecaborates have been produced through various methods but these methods have been unable to produce high levels of decahydrodecaborate, the more valuable of the two polyhedral boranes. As decahydrodecaborate and dodecahydrododecaborate are often produced together, separation must be provided for the pure products. Previous methods of separation have been labor intensive.
Therefore, there is a need for a process for producing polyhedral boranes in good yields and in a safe and efficient manner compatible with large scale production.